Good carbs, bad carbs? Should we really be concerned about the GI of what we eat, or is this yet another passing food fad? We sort the science from the hype.(Report: glycaemic index (GI))(Cover Story)

Publication: Choice (Chippendale, Australia)

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COPYRIGHT 2004 Australian Consumers' Association

IN A NUTSHELL

* Despite the claims, there's not yet conclusive evidence that low-GI foods are either generally health-promoting or slimming. The whole theory of the GI of foods affecting your health is still very much 'work in progress'.

* If you want to give GI a go, don't choose foods based on their GI alone--look at their overall nutritional value.

* But GI is good news for people with diabetes, both with Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent).

We're used to the idea of good fats and bad fats. Now, it seems, some carbohydrates might be healthier for us than others.

The glycaemic index, or GI, is a way of ranking carbohydrate foods according to their effect on blood glucose. Foods with a low GI (such as whole grains, pasta and most legumes) make out blood glucose rise and fall gently. High-GI foods (such as white bread and potatoes) are broken down quickly by our bodies and cause the blood glucose levels to surge and then crash. Some nutritionists now think these surges in blood glucose can affect our long-term health.

The diet gurus are leaping onto the GI bandwagon. Popular books and magazine articles are appearing on the subject, and GI claims are appearing in food ads and on labels (see Dodgy claims, page 12). High-GI foods such as bread and potatoes are roundly condemned as causing obesity, heart disease and diabetes. What's behind it all and how much of it should we believe?

WHICH FOODS HAVE A LOW GI?

GI's a complex concept and it's not simple to pick which foods have a low or high GI. Factors that influence the GI include:

* The type of starch in the food. Some types of rice, for example, have a high GI (regardless of whether they're white or brown)--but basmati rice, which has a different type of starch, has a medium GI.

* Cooking and processing. How the food is prepared and whether it's in big chunks or broken down into fine particles influence how fast it's digested. Pasta, for example, has a low GI probably because the starch is trapped in a sponge-like matrix of protein molecules in the pasta dough.

* The amount of fat. Fat slows the rate at which the stomach empties, and so slows the rate of digestion. Many fatty foods that are definitely unhealthy nevertheless have low GI values.

* The acidity of the food. Acid foods like vinegar, lemon juice, vinaigrette dressing and acidic...

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